The present invention relates to electronic timepieces whose time base frequency can be adjusted by means of a digital frequency correction circuit. The invention concerns more particularly an electronic timepiece or watch including means for producing time base pulses, a frequency divider which receives said time base pulses, a rate correction circuit connected between said time base producing means and said frequency divider for modifying the number of pulses received by the frequency divider during a predetermined period of time by a predetermined number of correction pulses, a driver circuit connected to receive the output signal provided by said frequency divider and a time display divider controlled by said driving circuit.
In such an electronic timepiece, the adjustment by steps of the frequency of the time base pulses is carried out by the addition or the suppression of a given number of correction pulses over a predetermined period of time. It can be seen that, in order to obtain a sufficiently fine step adjustment of the frequency of said time base pulses, a sufficiently long period of correction must be used. A simple calculation shows that when the frequency of said signal is 16.384 Hz, the correction period must be equal to 20 seconds if an adjustment step of .+-.1.5 10.sup.-6 is required.
In general, the frequency of the time base of an electronic timepiece is measured by an apparatus which measures the time elapsed between the first and the n.sup.th pulse of the low frequency signal which controls the display system of the timepiece, for example a stepping motor, n being a predetermined integer. The apparatus compares the value of the elapsed time given by the timepiece with a reference time interval, also called the integration period, in order to determine the frequency of the time base, i.e. the accuracy of the timepiece.
Now, if the addition or the suppression of correction pulses is made at each correction period, it is easy to see that, in order to obtain a precise measurement of the frequency, an apparatus having an integration period equal to said correction period is required. The integration times are standardized, while the correction period can vary from one timepiece to another, depending upon the desired accuracy of the frequency adjustment step, or upon the internal design of the timepiece. Therefore, if this condition is not fulfilled, it will be impossible to test the timepiece by a standard measuring apparatus.